Sewage purification treatment



Nov. 3, 1953 J. w. HOOD 2,658,034

SEWAGE PURIFICATION TREATMENT Original Filed Jan. 5, 1949 4 Sheets-Sheet l Q lu 2Q g Si s 'q r L n b Q it: v:

w N N A fj/J Nauw/Mmmm Na! Ngyowxf/ f f INVENTOR. fdl/11' )if 5004 Nov. 3, 1953 J. w. HOOD SEWAGE PURIFICATION TREATMENT 4 Sheets-Sheet 2 Original Filed Jan. 5, 1949 Patented Nov. 3, 1953 UNITED STATES RATENT OFFICE Divided and this application. October 17, 1950, Serial No. 190,579

2 Claims.

tion and controlled inoculation of the solution U With nitrifying bacteria and clarification by sedimentation over suicient time for the culture of the said bacteria and for general aerobic development.

The aeration introduces oxygen to the raw material at a point in the primary clariiier or in a separate culture tank which may follow the clarifier, the introduction being by means oi a mechanical device or system such as a submerged diilused air installation, or vacuum tuyre equipment. suspended above the liquid surface, or any other aeration device.

The introduction of inoculum containing nitrifying bacteria to the aerated liquid subject is preferable by means of a recirculation of a relatively small part of the eiuent from the biological oxidation means, the present treatment creating conditions in this eiuent favorable to this inoculation and requiring normally a recirculation of only about a quarter of the raw material iniiow.

An adequate contact period for the culture oi the nitrifying bacteria and general aerobic development (including aerobic types symbiotically related to the nitrifying bacteria) is provided mainly in the now through the initial clarifying stage during which the heavier solid matter is settled out as sediment, or in the subsequent culture tank. y

In the accompanying drawings illustrating th invention Fig. 1 is a curve sheet showing the conditions for most effective purification by the present system;

Fig. la is a diagram showing a typical system of sewage treatment;

Fig. 1b is a diagram similar to Fig. la and illustrating modications;

Fig. 2 is a diagram illustrating one aspect of the system of Fig. la;

Figs. 2a and 2b are diagrams of systems similar to that shown in Fig. 2 but somewhat modilied;

Fig. 3 is a diagram of a modified form of system; and

Figs. 3a, 3b, 3c, 3d and 3e are diagrams of systems similar to that shown in Fig. 2 but somewhat modied.

I have found that the solution, such as sewage and various waste liquors, prior to its entry into the biological oxidation means, should for best results be brought to a critical alkalinity and pH which is not substantially above the carbonate equilibrium curve A-B shown in Fig. 1. This curve shows the pl-I value at which calcium carbonate can exist in equilibrium in an aqueous solution and the term carbonate equilibrium curve as used herein and in the claims is employed in this sense. With the solution entering the biological oxidation means at point 4 above the carbonate equilibrium curve the preconditioning of the solution should be such that the oxidation action 4*-5 will modify the pH and alkalinity to bring 'these to a point 5 below the curve A-B and toward the decolloiding curve designated C-'D on the drawing about one pI-I below 'the curve A-B. It is only under these conditions that an ei-Hcient decolloiding can take place.'

Whenever the raw influent to be treated changes to bring about a departure from these preconditions, the pretreatment itself must be modiiled to restore they proper culturing with oxygen and nitrifying bacteria to insure that the eluent from the biological oxidation means is at 'a point on or about the decolloiding curve C-D.

With this recirculation providing inoculum and with the simultaneous aeration of the culture for an adequate contact period, the sewage entering the biological oxidation means is brought to a ,pl-I and alkalinity sufiiciently close t'o the' carbonate .equilibrium curve A-B so that the subsequent action in said means will carry the pH and alkalinity into proximity withor even belowthedecolloiding curve C-D. Results short of crystal clarity may be obtained slightly above the decolloiding curve C--D; for instance, the eiuent at point 5`of Fig. la is clear but not crystal.

In the system illustrated in Fig. la, the influent sewage at I0 enters the primary clarifierA l l removing the heavier sediment and' passes on to an aeration of inoculum through conduit I3 from a point following the biological oxidation means I5, and at the same time the air for aeration is diffused in from supply line I4. After being detained for a sufficient contact and culture period in tank l2, the preconditioned sewage is passed on to the biological oxidation means I5. This may be, for instance, a trickling filter distributing the flow over stone or sand media coated naturally with a zoogloeal film for the oxidizing and purifying action. From this the puried effluent is passed on to the final clarifier I6 from which the final eiuent is discharged at Il'. The supply of inoculum for the conduit I3 may be drawn either from the outfiow of the biological oxidation means at I 8 as shown in Fig. 2, or from the final effluent at I9 as shown in Fig. 2a, or from the final clarifier indicated at 20 as shown in Fig. 2b.

Irr some installations the condition of the sewage as to initial equilibrium is sufficiently low to dispense with the separate aeration-detention tank I2 and permit the culture to be developed in the primary clarifier II, the inoculum and air supplies I3, I4 being delivered to the clarifier sewage preferably at the entrance to the clarifier I I, as shown in Figs. 3, 3a and 3b, so as to allow an adequate contact period for the preconditioning in advance of the biological oxidation step.

To aid in this preconditioning the aqueous solution at entrance may, for instance, be supplied with a predetermined amount of effluent from the biological oxidation means in quantity sufficient to reduce the pI-I and alkalinity to within reach of effective filter action.

When this preconditioning has thus developed the culture of nitrifying bacteria and adiusted the pI-I alkalinity equilibrium to such a level that the action of this preliminary treatment has brought the mixture to or below the carbonate equilibrium curve and the biological oxidation means then carries the solution to a point near the decolloiding curve C-D, this biological filter action is eicient to lgive effective decolloiding. because in the zoogloeal film on the filter surfaces the nitrifying bacteria are preserved through the whole or a larger part of the filter bed and these bacteria have favorable conditions for their growth,

Nitrifying bacteria are numerically7 weak in ordinary sewages, only 100 per milliliter being typical. An additional supply of these bacteria for raw sewage inoculum purposes is therefore essential and an adequate oxygen supply is a basic requirement of the environment of these bacteria. The inoculum and the air or oxygen supply together with the proper preconditioning as to pH and alkalinity are therefore necessary to the effective action of the biological oxidation means, together with the thorough mixing and maturing of these preconditions bringing the nitrifying bacteria into thorough association with the material in solution,

Two distinct processes occur in a biological oxidation means such as a trickling filternamely (1) the removal of carbonaceous compounds by the oxidizing aerobic bacteria and (2) the conversion of ammonia and ammonia compounds by nitrifying bacteria, the carbonaceous removal normally taking precedence over nitrification. overloading of the biological oxidation means I have found to be at the expense of the nitrifying bacteria, the level of their action in the bed of the said means receding downward and eventually moving out altogether as the bed is progressively overloaded. In such case the biological oxidation means functions Substantially as a carbonaceous removing agency, the work done being represented on Fig. 1 of the drawings as an increase upward from 20 to 2| rather than downward. The effluent in such circumstances cannot be satisfactorily decolloided in the biological oxidation means withoutl further preconditioning.

Considering the raw sewage represented by the point 20 of plant X, instead of raising the pH and failing to desirably precondition the effluent as indicated by the line 20, 2|, the system of this invention during the treatment before biological filtration aerates and cultures the material and at the same time reduces the pH for instance as shown by the line 20, 22 (Fig. l).

Therefore, starting with the raw sewage equilibrium at a peak strength of pH 7.4 and alkalinity 190 p. p. m. M. O. and assuming existing plant of predetermined filter capacity, the raw inflow is admixed with a quantity of filter effluent either in the primary clarifier I I or the aeration-detention tank, of approximately 20% by volume. This serves the double purpose of inoculating with raw material with active bacteria agents from the filter and also gives a slight downward equilibrium adjustment 20, 22 as shown in Fig. 1. From the time that the recycled material is introduced to the raw subject, dissolved oxygen should be maintained to a minimum concentration of 2 p. p. m. all the way to the point where the culture mixture reaches and is applied to the filter or other biological oxidation means. Under this active encouragement of the culture I have found the filter adjustment downwards in terms of pH and alkalinity about in the neighborhood of 0.4 pH and p. p. m. alkalinity, so that be ginning from a point 22 slightly below the carbonate equilibrium curve AB, the filter effluent reaches a point 23 near to the decolloiding curve C-D, or approximately 1 pH below the curve A-B.

This adjustment as above accomplished by the proper culturing of the raw material as to inoculum, aeration and time, followed by the biological oxidation under the favorable conditions established by the preconditioning and very complete removals of organic and mineral content are at the same time attained. The aesthetic value of the subject, when expressed in p. p. in. turbidity, is greatly enhanced, the turbidity approaching zero and being clear or even crystal-clear sufficiently close to the decolloiding curve C--D.

Considering a plant Z, with a raw subject of equilibrium and organic strength corresponding to the point 3l] (Fig. l), the application of this to a filter or biological oxidation means under these conditions of bicarbonate alkalinity and hydrogen ion concentration will result in little or no purification regardless of the dosing technique which leaves the subject at or near the point 30. I have found that such material in accordance with the filter performance as above explained must be brought to a lower point of equilibrium in the neighborhood of the equilibrium curve and at the same time must be seeded and cultured by inoculation and aeration so as to be in a condition favorable for the preservation and propagation of the culture on the zoogloeal film by the biological oxidation means. The raw subject at the point 3D is therefore subjected to increased recirculation of the effluent through conduit I3 and intensified and protracted aeration, bringing the equilibrium before filtration down to the point 4. The recirculaton ratio is about one to one and the dissolved oxygen is maintained slightly above 2 p. p. m. resulting in a readjustment by virtue of this recirculation and dilution to bring the point of equilibrium of the filter influent slightly above the carbonate equilibrium curve A-B. The biological oxidation means then will automatically carry the equilibrium down further to the point where the eiiiuent is very clear and quite acceptable, but not to sparkling clarity such as would be attained at a point on or very close to the decolloiding curve.

The amount of recirculation is related to the conditions of inoculation and culture, the longer the culture period the less the required recirculation. For instance, in the performance exempliiied by plant Z at points 30, i and 5, the detention period allowable in the tank l2 was only in the neighborhood of ten minutes and this necessitated a large recirculation in the neighborhood of a one to one ratio, which recirculation in turn was responsible in part for the relatively short detention period. A longer culturing period, for instance of one hour, would with greatly decreased circulation depress the equilibrium even more effectively, and produce improved clarity in the eiuent from the biological oxidation means. In such improvement of the culture conditions by increase in the culture time, the entire performance would swing more to the vertical, bringing the filter eluent well below the desired point of equilibrium and. producing results of superlative quality.

To demonstrate the' effect of the pretreatment-s, the plant Y may be referred to with its raw subject initially conditioned as indicated at the point 4i? from which with the usual recirculation and improper preconditioning the biological oxidation treatment as by nltration would be unproductive of any substantial purication proceeding usually along the lines il to 4l. Taking this same subject and assuming a given installation where the time of seeding and aeration is limited, the inoculation and maintenance of oxidizing conditions will depress the equilibrium along the line ill to 42 to the point 152 prior to the biological oxidation which then will carry the material along the line i2 to i3 to the point 43 near to the decolloiding curve C with the effluent clear but not or crystal clarity. In such a system increase in the cultural period, preceding the biological oxidation, might result either from a lower rate of raw influent or an increase in the size of a clarifying and culturing equipment with a corresponding improvement in the preconditioning of the nitrifving bacteria and a depression of the equilibrium along the line 4i! to de to the point 44 prior to the biological oxidation. With this longer aeration and culture period, a better conditioning of the nitrifying bacteria is attained and the biological oxidation will continue along the lines M to 45 at a relatively higher rate of nitriflcation, bringing the point i5 substantially on the decolloiding curve C-D to give a crystal clarity in the eiiiuent of the biological oxidation step.

Various other modications of the system may be resorted to, for instance as diagrammed in Figs. lb, 3c, 3d and 3e. In this particular flow diagram the raw sewage of untreated waste through conduit 53, 53 is discharged into a preliminary settling tank 54 which may be preceded by the conventional types of grit removal and screening to take out the heavy inorganic solids and remove or break up the large particles. In the primary tank 54, the solids in form for readily settling are removed and the settled liquor is discharged to a biological oxidation means 58 such as a trickling nlter. In this biological oxidation means 58 the waste is acted upon by bacteria and other organisms in presence of oxygen to reduce and change the dissolved and colloidal substances in the waste so that they will readily settle out in the secondary clarifier 6G. The liquid is passed from this biological oxidation means 58 through conduit 5S to the nal clarier 6u for further settling out the decolloided solids, the effluent from this tank G being passed by conduit 6l to final disposal. In order to secure the proper conditions in both the primary settling tank 5d and more particularly in the biological oxidation means et, nitrifying bacteria are taken from some point after this biological oxidation means 53 such as the inuent to the secondary clariiier at 62, as shown in Fig. 3c, the conduit from the secondary clarier at 63, as shown in Fig. 3d, or the nal eiiluent at Gil, as shown in Fig. 3e, and introduced through conduit E35 into inoculum culture tank 52 or the conduit 5t carrying the raw infiuent. Where these nitriiying bacteria are physically or numerically weak, this inoculum conditioning tank 52 or the primary clarier 5i Will provide the proper environment to stimulate the growth of these nitrifying bacteria to such a point that proper environmental conditions may be maintained in the primary clarier 5i and biological oxidation means 58 by providing an inoculum which will contain a numerically large concentration oi strong and active organisms. In the inoculum conditioning tank 52 proper environmental conditions for strengthening and concentrating inoculum may be provided by aeration through pipe 5B, and it is important that ample` food supply be provided to allow these bacteria to build up. This food supply may be provided by means of by-passing a certain portion of the raw sewage ow from inflow '50 through conduit 5| to the inoculum conditioning tank 52 or the addition of an auxiliary food supply in the form of chemicals or other substances. It Will also be understood that it will be possible to build up the proper inoculum by providing auxiliary nitrifying bacteria and/or chemicals or other substances to produce the proper environment for rapid growth of these bacteria in the conditioning tank. The inoculum may be introduced into the treatment systemy by conduits 5S, 5l ahead of the primary settling tank 54 or directly ahead of the biological oxidation means 5S through conduit 56,

'air being introduced to the primary clarier 5d at 6l. The point of application of the invention 'will depend upon the condition and characteristics of the waste to be treated, and bypass 66 may be used to pass the inoculum directly to the conduit 5t from the conduit 65.

By introducing the concentrated inoculum from culture tank 52 it is possible to increase the activity in the 'biological oxidation means.

The system of this invention therefore comprises the creationof an environment favorable to both the aerobic carbonaceous bacteria and the nitrifying bacteria by the introduction of oxygen to the raw subject and the introduction of inoculum containing nitrifying bacteria mixing of the inoculum in said subject so to insure complete dispersion and with this the downward adjustment of the carbonate eouilibrium by returning additional amounts of nal filtrate to the raw subject if and as required so as to insure that said subject shall be in a zone of carbonate equilibrium at the filter influent favorable to complete subsequent biochemical oxidation action or filtration.

I have found that where the lter design, as in prevailing practice, is based on B. O. D. loadings per unit volume of lter media the operation is unsatisfactory. There is no constant relation between the B. O. D. and the carbonate equilibrium so that the former is not to be depended upon as the basis of the treatment required to condition the subject for biological oxidation to produce the desired degree of treatment.

Under the system of this invention the conditions are favorable to the oxidation of ammonia and the oxidation of carbonaceous compounds is always necessarily present and complete decolloiding occurs in the biological oxidation means following the preconditioning. This decolloiding also necessarily reduces the B. O. D. because the treatment has substantially divested the subject of colloidal and other suspensions by consumption of the putrefying bacteria and other unstable matter by the aerobic bacteria.

The system of this invention therefore surely and efficiently attains the desired complete purification. The preconditioning and purification may often be expeditiously carried out even under limitations of available equipment providing the raw subject can be given suicient time, aeration and recirculation before the biological oxidation means, which is usually of ample capacity for a properly preconditioned subject.

Additional economy is effected where, as is preferred, the recirculated eiiiuent is drawn from the final clarifier at a point carrying with it the solids so that there is no separate digestion of this final sedimentation. The inclusion of these solids in the recirculated liquid also contributes to the effective action of the process in preconditioning the material for the biological oxidation means I5.

The nitrifying bacteria as well as the other oxidizing organisms are continuously cultured and maintained throughout the cycle including the recirculation. The interval of transfer of the recirculated portion from the filter treatment to the admixture of air is very short, not more than fifteen minutes and generally much less, and the prompt renewal of the supply of oxygen is in sufficient amount to insure a dissolved oxygen content at all times above the minimum of two parts per million and at the area of mixture of the order of six parts per million.

At design loading (volumetric) the period in the aeration-detention tank or primary clarifier in admixture with the oxygen supply allows preferably not over one-half hour for air mixing and one or, in some cases, two to three hours or more for culture or for culture and clarification, and within this time the effect of the process brings the pH and carbonate alkalinity' to or below the carbonate equilibrium curve A-B. The B. O. D. of the influent is also reduced by 50 to 80% in advance of the main biological oxidation means I which thus receives the inflow in ideal condition for its operation. This biological filtration, therefore, starts with the material reduced in B. O. D. by 50 to 80% and the pH and bicarbonate alkalinity are at or below the critical carbonate equilibrium curve A-B irrespective of the initial condition of the raw sewage so that the functioning of the biological ltration at I5 is in the region below the curve A-B and this automatically maintains the proper and efficient conditioning and distribution of the nitrifying bacteria and other oxidizing organisms to attain the desired clarity of the effluent in the neighborhood of the decolloiding curve C-D. This with the accompanying purification attains a final eiiluent completely treated in that it is substantially divested of colloidal and other suspensions and also has a low B. O. D. and high stability.

This case is a division of my application Ser. No. 69,379, iiled January 5, 1949 as a continuation-in-part of my prior application Ser. No. 514,831, filed December 15, 1943, now abandoned. Application Ser. No. 69,379 is now Patent No. 2,529,295.

I claim:

l. A process employing trickling filter means for treating sewage and. other aqueous wastes consisting in supplying an influent of said material to a primary clarifier by sedimentation in advance of the trickling filter, intermixing with the flow between the primary clarification and the trickling filter a supply of treated material recirculated from a later stage of the process following treatment of the material by biological oxidation maintained at a dissolved oxygen content of at least two parts per million and simultaneously with said supply of treated material introducing and intermixing with the flow from the primary clarification to the trickling filter an aerating supply of oxygen-containing gas, subsequently subjecting the clarified material with a gradually increased surface exposure to a further supply of aerating oxygen-containing gas in a trickling filter raising the dissolved oxygen content further above said two parts per million for a correspondingly increased biological oxidation, drawing off a portion cf the eiiluent from said trickling filter and passing said portion back for recirculation as said supply of treated material for mixture with said flow at a point subsequent to said primary clarification and between said primary clarification and said trickling filter, and continuing said treatment of the material under biological oxidation in the presence of a desired oxygen content of at least two parts per million.

2. A process employing trickling lter means for treating sewage and other aqueous wastes as set forth in claim 1 in which an intermediate aeration detention tank intcrvenes between the primary clarifier and the trickling filter and receives the supplies of recirculated treated material and aerating oxygen-containing gas.

JOHN W. HOOD.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date Re. 22,144 Ward July 2l, 194?. 1,994,887 Downes et al Mar. 19, 1935 2,154,132 Mallory Apr. 11, 1939 2,180,148 Imhoff Nov. 14, 1939 2,364,298 Kamp Dec. 5, 1944 2,517,792 Kraus Aug. 3, 1950 2,528,887 Kiekhoefel et al. Nov. 7, 1950y 2,529,295 Hood Nov. 7, 1950 2,562,510 Schlenz July 3l, 1951 

1. A PROCESS EMPLOYING TRICKLING FILTER MEANS FOR TREATING SEWAGE AND OTHER AQUEOUA WASTES CONSISTING IN SUPPLYING AN INFLUENT OF SAID MATERIAL TO A PRIMARY CONECT BY SEDIMENTATION IN ADVANCE OF THE TICKLING FILTER, INTERMIXING WITH THE FLOW BETWEEN THE PRIMARY CLARIFICATION AND THE TRICKLING A SUPPLY OF TREATED MATERIAL RECIRCULATED FROM A LATER STAGE OF THE PROCESS FOLLOWING TREATMENT OF THE MATERIAL BY BIOLOGICAL OXIDATION MAINTAINED AT A DISSOLVED OXYGEN CONTENT OF AT LEAST TWO PARTS PER MILLION AND SIMULTANEOUSLY WITH SAID SUPPLY OF TREATED MATERIAL INTRODUCING AND INTERMIXING WITH THE FLOW FROM THE PRIMARY CLARIFICATION TO THE TRICKLING FILTER AN AERATING SUPPLY OF OXYGEN-CONTAINING GAS, SUBSEQUENTLY SUBJECTING THE CLARIFIED MATERIAL WITH A GRADUALLY INCREASED SURFACE EXPOSURE TO A FURTHER SUPPLY OF AERATING OXYGEN-CONTAING GAS IN A TRICKLING FILTER RAISING THE DISSOLVED OXYGEN CONTENT FURTHER ABOVE SAID TWO PARTS PER MILLION FR A CORRESPONDINGLY INCREASED BIOLOGICAL OXIDATION, DRAWING OFF A PORTION OF THE EFFLUENT FROM SAID TRICKLING FILTER SAID PASSING SAID PORTION BACK FOR RECIRCULATION AS SAID SUPPLY OF TREATED MATERIAL FOR MIXTURE WITH SAID FLOW AT A POINT SUBSEQUENT TO SAID PRIMARY CLARIFICATION AND BETWEEN SAID PRIMARY CLARIFICATION AND SAID TRICKLING FILTER, AND CONTINUING SAID TREATMENT OF THE MATERIAL UNDER BIOLOGICAL OXIDATION IN THE PRESENCE OF A DESIRED OXYGEN CONTENT OF AT LEAST TWO PARTS PER MILLION. 